Process for making a copper-chromiumzirconium alloy



United States Patent 3,194,655 PROCESS FOR MAKING A (IQPPER-CHROMIUM-ZIRCONIUM ALLOY Alan R. Pels, Stamford, and Herman F. Petsch, Newtown,Conn, assignors to National Distillers and Chemical Corporation,Richmond, Va., a corporation of Virginia No Drawing. Fiied July 28,1961, Ser. No. 127,477 3 Claims. (Cl. 75-435) This invention relates tocopper-chromium-zirconium alloys.

' The object is to provide such an alloy with its componentsproportioned to provide the maximum possible degree of high electricalconductivity, resistance to undue softening when working at high servicetemperatures, such as in the vicinity of 400 C., and high notch strengthor toughness.

The above properties are desirable when the alloy is used to makecommutator segments for electric motor armatures which must operate athigh rotative speeds and high temperatures. They are also desirable whenthe alloy is used for brazing or welding in the case of work which inservice must conduct electricity while mechanically stressed under hightemperatures. The desirable properties of the new alloy make its useadvisable whenever these properties are an advantage.

The prior art has suggested in general terms the addition of zirconiumto copper-chromium alloys. However, this has been insufiicient to teachthe art enough to permit the production of an alloy suitable forcommercialization. Commercially there are only the copper-zirconium andcopper-chromium alloys available for use as electric conductorsoperating under high stress at elevated temperatures and comparableservice. The former is lacking in strength, while the copperchromiumalloy lacks notch toughness and resistance to undue softening at hightem peratures.

According to the present invention the object stated hereinabove isattained by an alloy consisting, by weight, of from .60 to .90% purechromium, .40 to .60% pure zirconium and withlthe balance pure copper.Insofar as is commercially possible, the alloy is free from oxygen inany form. For use it is solution heat treated and quenched, and thenordinarily it is cold worked and aged. Such processing may be varied.The components are pure to the degree that this is now commerciallypossible, and the alloy is free from other components excepting possibletraces.

Within the above compositional ranges, it follows that the chromiumcontent cannot be less than the zirconium content. Furthermore, thezirconium must be present in metallic form as contrasted to zirconiaresulting from the use of zirconium for the purpose of de-oxidizing acopperchromium alloy. The best possible results are believed to beobtained with an alloy consisting of .75% pure chromium and .50% purezirconium, the balance of course being pure copper and the alloy beingoxygen free.

To make certain that the zirconium is present in its metallic form, anyoxygen present in the copper prior to the addition of this alloyingcomponent should be removed by de-oxidation. Casting of the melt shouldbe done so as to avoid an oxygen pick-up.

The new alloy has been made in the following manner:

The copper may be cathodic copper, OFHC copper or tough pitch copper,all of which are substantially pure. The copper is melted down whileprotected from oxygen, as by being kept under a cover of charcoalfloating on its surface. Its temperature is brought to about 1100 C. andit is then de-oxidized by adding small amounts of any suitablecommercial de-oxidizer that would ordinarily'be used to scavenge oxygenfrom copper. A calcium-lithium type is suitable. The temperature is thenraised to about 1500 C., when the copper is again de-oxidized.Throughout this procedure good metallurgical techniques are used toobtain an oxygen free copper that is free from everything exceptpossibly traces of the de-oxidizer or de-oxidizers used.

With the copper at about 1500 C., the selected amount of chromium isadded. This may be in the form of pure chromium powder wrapped in purecopper foil. Commercial copper-chromium master alloy may also be used,containing from 5 to 10% chromium with the balance copper. This additionis made through the charcoal cover. The melt is held at about 1500 C.long enough to make certain that the chromium is completely dissolved inthe copper, this high temperature having the advantage of reducing thesolution time.

Next the melt is permitted to cool to about 1300 C., this temperaturebeing high enough to provide rapid solution of the zirconium and is ofvalue in reducing the zirconium loss due to possible small amounts ofoxygen which may be present in the melt in spite of the precautions usedto avoid this. The selected amount of pure zirconium is added at thistime. This may be in the form of copper-zirconium master alloycontaining about 33% zirconium with the balance copper. Again for thepurpose of making as certain as possible that zirconium loss is avoided,the melt is poured just as soon as the zirconium goes completely intosolution. It is possible t top pour the melt while holding the charcoalcover back.

It is believed to be preferable to protect the melt against oxygen whilepouring. However, it has been f und that if the pouring time is short,and the pouring stream is kept solid, as contrasted to spraying, suchprotection is not mandatory. The cast metal may be permitted to solidifywithout requiring any particular protection from oxygen since the topsurface exposed to the atmosphere is ordinarily of relatively smallarea. In any event, any oxygen picked up by the top of the casting islocalized and does not affect the balance of the casting.

After solidification the casting is extruded at temperatures of about930 C. This temperature is used not only to permit extrusion withoutusing excessive extrusion force, but also because it assures keeping thechromium and zirconium in complete solution with the copper. Instead ofextrusion, hot rolling or forging is also possible. After such workingthe alloy is air cooled.

In the actual Working of the present invention the casting is extrudedto a rectangular shape that is 2" wide and .50" thick. It is air cooledafter extrusion largely as a matter of convenience. Thereafter it issolution heat treated by being heated to about 950 C. for about 1 /2hours. The shape is actually in the necessary furnace somewhat longer,the 1 /2 hours time period being while the metal is actually at 950C. Atthe end of the described time period the metal is quenched in water tokeep.

the chromium and zirconium in solution with the copper.

components might come out of solution.

as The extruded shape'is thencold rolled to .25" thickness, its 2" widthremaining the same. It is thereafter given a treatment corresponding tothat already describ d and after that the shape is further cold rolledto .100" thick, its width again remaining at 2". Then to make absolutelycertain that the chromium and zirconium are in solution, the .100" thickmaterial is solution heat treated ing the material is aged by heatingitto 1 hour, at temperatures ranging from 450 C. to 600 C. A specificexample of the results achieved is as follows: The specimen had acomposition of .60% chromium, .45 zirconium and the balance copper. Thechromium and zirconium were present in pure metallic form and the alloycontained no appreciable or easily measurable amount of oxygen in anyform. It was substantially free from anything other than specified, withthe understanding that the balance was, of course, pure copper. In thisinstance the material was rolled to the .04" thickness from which /2"wide specimens were cut.

7 These specimens were given varying ageing heat treatments so thatthey'broke down into the following categories:

A-As cold rolled only BAs cold rolled only and aged for 1 hour at 450 C.C--As cold rolled only and aged for 1 hour at 600 C.

These three specimens showed the following conductivities:

A=35.5 B=73.6 C =81.2

ageing treatment and result in softness at both room and hightemperatures. With this in mind the following hardness values wereobtained:

ARockwell B 82.0

B-Rockwell B 84.0 C-Rockwell B 76.0

Tensile testing at room temperature produce the following values:

A--61,700 p.s.i. lit-76,000 p.s.i. C61,350 p.s.i'

Elevatedtemperature tensile testing of the B specimen showed at 450 C. atensile strength of 53,500 p.s.i.

In addition to the above, one of the B specimens was cut to a .700"width and had 60 degree V-notches formed in its edges reducing its widthat the roots of the two notches to .500". This notched B specimen whentested at 450 C. showed a tensile strength of 56,600 p.s.i.

Two C specimens were also tensile tested at 450 C., one being unnotchedand the other notched as just described in the case of the Bspecimen. Inthis instance the unnotched specimen showed a tensile strength of 40,900p.s.i. and the notched specimen showed 45,250

p.s.i.

It can be appreciated from theforegoing that the object of the inventionis achieved by the compositional balance described in conjunction withthe use of good practices assuring that the resulting alloy isfree from4L oxygen-and other than mere traces of de-oxidizers and the likewhic'rrare unavoidable.

It is necessary to keep the composition within the ranges specified. Itthe chromium is permitted to drop below the .60% minimum the mechanicalproperties reduce without a proportionate gain in electricalconductivity. Chromium above .90% causes an excessive loss in electricalconductivity without a proportionate gain in mechanical properties. Ifthe zirconium dropsbelow the .40% minimum or goes above.60% theresistance to high temperatures suffers. V

Finally, if the chromium content is reduced'to less than the zirconiumcontent, then at high temperatures,

, such as around .400 C. or higher, the tensile properties drop to asubstantial degree thus indicating undue softness when the alloy is inservice at such high temperatures.

Although the alloying, heat treatment, and other processing have beendescribed in some detail, itis believed possible to vary these somewhat.It is necessary, neglecting traces of de-oxidizers, etc.', to obtain analloyconsisting only of from .60 to '.90% chromium,".40 to .60%zirconium, balance copper. Oxygen is avoidedas much as possible keepingin mind that the zirconium inparticular has a great tendency to combinewith oxygen. The new alloy requires that the zirconium, and the chromiumalso, be in metallic form and thoroughly in solution with the copper. Ifthese precautions are observed, it is be lieved that the new alloy maybe handled generally in the manner of the old copper-chromium andcopperzirconium alloys, with theresulting new material avoiding thedisadvantages of both of these old alloys. Ordinarily, the new materialwill be solution heat treated, to assure the condition of completesolution of its components, and it would ordinarily be cold worked totemper it somewhat and then, by the meet heat and time, aged toenhahceits physical and electrical properties to the optimum degree.

We claim:

1. A process for making a copper-chromium-zirconium alloy, comprisingforming a melt of substantially pure oxygen freecopper protected fromoxygen, while maintaining said melt so protected and at a'hightemperature completely dissolving therein from .60 to .90% chromium,thereafter while so protected lowering the temperature of said melt to atemperature causing rapid :solution of zirconium therewith withoutexcessive zirconium loss and dissolving therein from .40%, to'. 60%zirconium and I with complete solution thereof promptly processing thealloy melt to form a casting.

2. A processfor making a copper-chromium-zirconium alloy, comprisingforming a melt of substantially pure oxygen free copper protected fromoxygen, while maintaining said melt so protected and at a hightemperature completely dissolving therein from .60 to .90% chromium,thereafter while so protected lowering the temperature of said melt to atemperature causing rapid solution of zirconium therewith withoutexcessive zirconium loss and dissolving therein from .40% to .60%'zirconium and with complete solutionthereof promptly processing thealloy melt to form a casting, and thereafter reducing said casting tothe shape and dimensions desired and solution heat treating this shape.l

3. A process formaking a copper-chromium-zirconium alloy, comprisingforming .a melt of substantially pure oxygen free copper protectedfromoxygen, while maintaining said melt so. protected and at ahightemperature completely dissolving therein from .60 to 30% chromium,thereafter while so protected lowering the temperature of said melt to atemperature causing rapid solution of zirconium therewith withoutexcessive zirconium loss and dissolving therein from .40% to .60%zirconium and with complete solution thereof promptly processing thealloy melt to form a casting, and thereafter reducing said casting tothe shape and dimensions desired and solution heat 5 treating this shapeand thereafter cold Working and ageing the shape.

References Cited by the Examiner UNITED STATES PATENTS 724,524 4/03Tilden 75-435 2,025,662 12/35 Hansel et a1. 75-153 2,066,512 1/37 Archer75153 2,254,944 9/41 Hensel et a1. 75--153 6 OTHER REFERENCES DAVID L.RECK, Primary Examiner.

RAY K. WINDHAM, ROGER L. CAMPBELL,

Examiners.

1. A PROCESS FOR MAKING A COPPER-CHROMIUM-ZIRCONIUM ALLOY, COMPISINGFORMING A MELT OF SUBSTANTIALLY PURE OXYGEN FREE COPPER PROTECTED FROMOXYGEN, WHILE MAINTAINING SAID MELT SO PROTECTED AND AT A HIGHTEMPERATURE COMPLETELY DISSOLVING THEREIN FROM .60 TO .60% CHROMIUM,THEREAFTER WHILE SO PROTECTED LOWERING THE TEMPERATURE OF SAID MELT TO ATEMPERATURE CAUSING RAPID SOLUTION OF ZIRCONIUM THEREWITH WITHOUTEXCESSIVE ZIRCONIUM LOSS AND DISSOLVING THEREIN FROM .40% TO .60%ZIRCONIUM AND WITH COMPLETE SOLUTION THEREOF PROMPTLY PROCESSING THEALLOY METAL TO FORM A CASTING.